A muffler designed for an exhaust system of an internal combustion engine of a motor vehicle, in which a heat exchanger unit is integrated in order to make it possible to transfer heat being transported in the combustion exhaust gases discharged by the internal combustion engine to a heat transfer medium, for example, to the cooling liquid flowing in a closed coolant circuit of an internal combustion engine, is known from DE 10 2012 104 396 A1. The muffler has an inlet pipe and an outlet pipe. A first flow path blocking/releasing member is associated with the inlet pipe, and a second flow path blocking/releasing member is associated with the heat exchanger unit. These two flow path blocking/releasing members can be brought, coordinated with one another, into such blocked or released positions that the combustion exhaust gas entering via the inlet pipe takes either a first flow path, in which it flows through the heat exchanger unit for heat transfer to a heat transfer medium and leaves the outlet pipe after flowing through the heat exchanger unit, or, to avoid such a heat transfer interaction between the exhaust gas and the heat transfer medium, it takes a second flow path, in which it does not flow through the heat exchanger unit and, after leaving the inlet pipe, it flows directly to the outlet pipe, bypassing the heat exchanger unit, and is discharged from said outlet pipe.
EP 2 733 322 A1 discloses a muffler with a heat exchanger unit integrated in same. The muffler has two inlet pipes and one outlet pipe. The exhaust gas leaving the internal combustion engine can be sent through the flow path blocking/releasing member via a first of the inlet pipes and thus a first flow path, in which the exhaust gas flows through the heat exchanger unit and can transfer heat to a heat transfer medium before it leaves the muffler via the outlet pipe. In another position of the flow path blocking/releasing member, the exhaust gas is sent via the second of the inlet pipes to a second flow path, in which it flows to the outlet pipe and leaves the muffler via the outlet pipe without thermal interaction with the heat transfer medium.
The problem arises, especially in motor vehicles with hybrid drives, that, on the one hand, the space available for the installation of an exhaust system and especially for the muffler or mufflers integrated in same is comparatively limited due to the batteries being accommodated in the bottom area. On the other hand, increasingly strict legal requirements require a reduction of the noises released by such a vehicle, which makes it, in turn, necessary to use larger mufflers. Furthermore, the internal combustion engines used in motor vehicles and especially in hybrid drives are so efficient that the waste heat provided by these during the combustion operation is frequently insufficient for a sufficient thermal conditioning of the interior of a vehicle. The use of comparatively large mufflers with heat exchanger units integrated in them for utilizing the heat being transported in the combustion exhaust gas is, however, difficult because of the crowded space conditions especially in the bottom area of such vehicles, taking into account the fact that there also are requirements imposed on the muffling properties.